A method for manufacturing an aluminum alloy cladding material has been conventionally carried out by, for example, hot rolling for joining as described below. First, a core material and a skin material are prepared according to a clad rate of interest. In general, for the core material, an ingot is faced to have a predetermined thickness. For the skin material, an ingot is faced, hot-rolled, rolled to have a predetermined plate thickness, and cut in accordance with the length of the core material alloy. Homogenization treatment of the core material is carried out if necessary, and the skin material and the core material are then joined, heated prior to hot rolling, and is rolled for joining by a reverse-type hot rolling machine. The core material and the skin material are press-fitted by the rolling for joining and rolled to have a thickness of interest after the press-fitting in such a manner that a usual aluminum alloy ingot is hot-rolled.
However, the hot rolling for joining requires rolling under low pressure for suppression of peeling and warpage of a plate until press-fitting strength becomes sufficient and is inferior in productivity to usual rolling. In addition, it is necessary for press-fitting aluminum alloy materials or pure aluminum materials (hereinafter uniformly referred to as aluminum alloy materials) to each other to mechanically demolish an oxide film on a press-fitted interface by deformation and to allow a newly formed surface to appear. Therefore, it is necessary to apply a load, sufficient for demolishing the oxide film on the press-fitted interface, to a portion that is farther from the contact surface of a roll when a clad rate is high, and there are also rolling machine facility limits. Thus, it is considerably difficult to manufacture a material with a high clad rate of more than 20% in the method for manufacturing a clad material by the press-fitting rolling. The degree of difficulty is also high for multilayered materials. For example, there is a method in which press-fitting rolling is divided into two or more processes, which are carried out. However, there are considerable troubles in the method.
Against the problems of the manufacture of a clad material as described above, Patent Literature 1 proposes a manufacturing method in which when a clad material of an aluminum alloy is manufactured, only the surface layers of joining materials are heated, and press-fitting rolling can be carried out at high rolling reduction rate while preventing a clad interface from peeling in rolling for joining. However, in Patent Literature 1, when press-fitting rolling is carried out under unexpected high pressure, since joining surfaces are not bonded to each other, warpage occurs, a press-fitted surface is peeled, and it can be impossible to manufacture a clad material.
A method for obtaining a clad material at a high clad rate is considered to be enabled by a method described in Patent Literature 2. Patent Literature 2 proposes, as a method for bonding metallic materials, a method of heating and pressurizing metal joining materials to be bonded, with an intermediate material, in which an element that is not melted into a parent phase in a solid state is scattered in a soft metal such as aluminum, therebetween, by rolling, extrusion, drawing, and/or the like. In the method, there are manufacture limits that it is necessary to apply strong downward pressurization in a temperature range in which the intermediate material melts. In addition, an element that has a low melting point and does not become a solid solution in a solid state is added to the intermediate material, and it is presumed that only a low-melting-point metal that exists on a surface can be used for bonding. Therefore, there is apprehension that an addition amount for obtaining sufficient bonding strength is considerably increased, a large amount of low-melting-point metal component remains in a bonded interface after bonding, and the characteristics of a metal base material are adversely affected.
There is also a method for manufacturing a clad material by face bonding by solid phase diffusion bonding or liquid phase diffusion bonding. In the solid phase diffusion bonding, long time is needed for bonding compared to welding, brazing, and the like since a diffusion phenomenon is utilized. In general, retention at predetermined temperature is needed for time of around 30 minutes or more. In addition, since pressurization is needed for bonding, complication of a bonding operation and increase in cost are inevitable. Further, in the case of an aluminum alloy material, since a stable, firm oxide film exists on the surface thereof and diffusion is inhibited thereby, it is difficult to apply the solid phase diffusion bonding. When the liquid phase diffusion bonding is used particularly in a large-scale industrial product, it is difficult to optimally control the amount of a remaining insert material to be a liquid phase after bonding the insert material, and it is also difficult to suppress the growth of an intermetallic compound generated in a portion to be bonded. Thus, it is difficult to keep favorable bondability in the liquid phase diffusion bonding.